A pioneer device of this general type is described and claimed in U.S. Pat. No. 3,304,560, granted to Adolph G. Kiefer on Feb. 21, 1967, assigned to the assignee of the present application and entitled "Turbulence-Reducing Device for Swimming Pools".
The Kiefer patent discloses a series of hollow cylindrical elongated bodies having perforated surfaces defined by a series of integrally molded plastic strips which criss-crossed each other in what may be called a lattice-work fashion. These bodies are confined in axial alignment by means of a line, or cable, attached at opposite ends of a swimming pool and maintained under tension for the purpose of holding the individual bodies substantially one-half submerged. In addition, since the assembly of lattice-like bodies and cable has a slightly negative buoyancy, floats are attached to the cable (or to the bodies) to assist in maintaining the bodies at a desired level in a body of water.
This assembly of bodies can be described as being designed to substantially eliminate the passage of disturbed water, caused by the efforts of a high-speed swimmer proceeding in one racing lane, from being transmitted to the next adjacent lane. This results from the fact that the turbulence of the wake produced by the moving swimmer is absorbed, or dampened, when it reaches the turbulence reducing bodies by the fact that the waves and troughs forming the wake are broken up and water is aerated reducing driving force of waves due to the perforated surfaces and portions of the kinetic energy in the wake is absorbed by efforts expended in rotating the turbulence reducing bodies which are freely rotatable about the restraining cable.
A later form of device of this general type is disclosed and claimed in U.S. Pat. No. 3,755,829 granted to Mercer Donald Walklet on Sept. 4, 1973, assigned to the assignee of the present invention and entitled "Turbulence Suppression Apparatus for a Body of Water". The wave suppression assembly comprises a continuous series of open-faced perforated discs, resembling spoked wheels, strung together in axially aligned relationship on a taut line, or cable, so that each of the elements is independently freely rotatable about its central axis.
One advantage of the assembly disclosed in the Walklet patent is, therefore, that it is more restrictive to irregular wake patterns, or eddy currents, than prior devices of the Kiefer type in which each of the freely rotatable elements comprised an elongated body. Thus, in the prior art, any force acting, for example on one side of an elongated turbulence reducing body and sufficient to effect movement of the body, created a slight counter turbulence back into the area from which the force acting was generated. In addition, the shorter length and larger diameter of the disc-shaped bodies disclosed in the Walklet patent, having greatly reduced mass, effectively reduces the inertia of each body and makes possible a more localized control of small disturbances in the water.
Further, using a large number of turbulence reducing bodies of individually short axial length means that, as a practical matter, there are no limitations on the dimensions of the racing lanes which can be protected, whereas in the earlier Kiefer assembly, in which each element was approximately a foot, or so, in length, a gap in the lane normally existed at every multiple of the element. This was because the length of the pool was rarely an exact multiple of the length of the element thereby creating an unfilled gap in the lane. The Walklet device, in having the axial length of each element preferably no more than an inch or two, allowed elements to be added, or subtracted, at will so that a continuous barrier along the sides of a lane can always be obtained regardless of the length of the lane in use.
However, a common feature of all of the foregoing prior art turbulence reducing systems is the provision of rotary baffle elements, or damping devices that depend, for their effectiveness, upon the generation of resultant opposite forces resisting the rotation of the damping elements for suppression of wave patterns creating turbulence. Since these two primary developments in the field, refinement has been in the nature of more sophisticated control of the rotation of the baffle elements. This has taken the form in some instances of providing limited resistance to rotation after an element has freely rotated through some angle, normally less than 90.degree.. In other instances elements have been created which are unbalanced as to their physical configuration and/or distribution of mass about their centers of rotation. Consequently, these elements tend to adopt a fixed position relative to a mounting cable and offer an extent of resistance to wave forces causing them to rotate.
These variations to the rotating element concept have not demonstrated an operational superiority, and, in some instances have introduced handling, strength, or other disadvantages.